Etching machine for curved plates and method



I Jan. 6, 1970 c. w. HOORNSTRA ETCHING MACHINE FOR 'CURVED PLATES ANDLMETHOD Filed march 39. 196 6 z/chm/ INVENTOR W. Hoe/fr) s/ra maxi flTTORNEY United States Patent US. Cl. 15614 4 Claims ABSTRACT OF THE DISCLOSURE An etching machine for the powderless etching of a curved plate comprises a rotatable cylindrical container having ends adapted to retain etching liquid therewithin, a rotatable circular array of longitudinal blades of arcuate cross-section positioned in spaced apart relationship within the container and longitudinally thereof, all the blades being coupled at respective ends to a header member by means for adjusting the angular rotation of each blade, the assembly of blades and headers being rotatable, a rotatable work holder adapted to support a curved plate during etching, said work holder being longitudinally disposed with respect to the cylindrical container and being centrally supported therein in inwardly spaced apart relationship to the circular array of blades, means for individually rotating each of the cylindrical container, the array of blades and the work holder, and inlet and outlet means for introducing and discharging etching liquid from the cylindrical container. An improved method of etching comprises rotating a liquid annulus of etching solution against a continuous internal wall of a cylindrical container, longitudinally positioning a rotatable curved plate to be etching inwardly from said liquid annulus and spaced apart therefrom, intercepting the inner surface of said liquid annulus with a circular array of curved longitudinally extending blades thereby impinging said liquid inwardly of the annulus toward the curved plate, said blades being adjusted at a predetermined rotational angle whereby the inwardly directed liquid impinges tangentially upon the curved plate, and rotating said curved plate on its axis rapidly enough to fling etching solution from the surface thereof.

This invention relates to the etching of metal by an etching fluid and more particularly concerns a new and novel etching machine having special utility in the powderless etching of curved plates or segments.

Ordinarily when metal cylinders, tubes, or curved segments having type and half-tone images photo-printed thereon are powderlessly etched by existing processes in existing machines, the typical result shows, to a greater or lesser degree, the following defects:

(1) Shoulder asymmetry; the image shoulders in circumferential directions are inordinately broad while those in axial directions are inordinately narrow or are even entirely absent so that two sides of the images are actually undercut.

(2) Channeling; circumferential channels are etched into the bottom of the plate between image areas.

(3) A phenomenon known variously as tailing, runaround, rundown or bleed-off in the vernacular of the trade; inordinately elongated shouldering occurs in circumferential directions from the boundaries of halftone image areas with non-image areas.

The primary object of this invention is to provide a new and unique etching machine for the powderless etching of curved metal photoengraving plates to minimize the problems and difficulties encountered in etching on the curve using prior art machines and processes.

Another object of the invention is to provide a curved plate etching machine which will etch curved plates or segments to provide a quality approaching that conventionally attained on fiat surfaces.

A further object is to provide a novel centrifugal etching machine which removes spent etchant from the curved surface being etched therein in a manner such as to prevent run off or tailing in the direction of. curvature.

A still further object of the invention is to provide a simple etching apparatus for powderlessly etching magnesium, zinc, and other base metal plates on the curve.

Another object of the present invention is to provide a new and novel method of etching curved plates.

The present invention will be readily understood from the following detailed description, especially when read in conjunction with the appended drawing wherein:

FIG. 1 is a plan view in section of a centrifugal etching apparatus in accordance with the present invention taken along line 1-1 of FIG. 2 and FIG. 2 is a side elevational view in section of the apparatus in FIG. 1 taken along line 22 of FIG. 1.

In general, the present novel apparatus comprises in combination: a rotatable cylindrical container closed at one end; an array of longitudinal blades uniformly circumferentially spaced apart, each blade being similarly bent about its longitudinal axis and having an arcuate cross-sectional configuration, said blades being spaced 4 from the container and being movably coupled at their ends to a common, circular, rotatable, header member; and a mandrel longitudinally and rotatably disposed in the apparatus in a spaced relationship to the blades, said mandrel being adapted to hold and rotate a curved plate.

Ordinarly there is also provided in the apparatus: drive means to rotate, singly or in combination, the container, blade and header assembly, and mandrel; and outlet means located in the lower portion of the apparatus from which to discharge spent etching solution and/or rinse liquids.

As an optional additional feature of the present novel apparatus, means may be provided either in or about the container for controllably cooling or heating of the etching fluid used in the apparatus.

In conjunction with the cooling and heating means, a temperature control and indicia means may be provided for ease and efficiency of operation. It should be understood, however, that the essential elements of the present novel apparatus comprise: a cylindrical container, a circular array of curved blades disposed therein in a spaced relationship to the container, and a longitudinal mandrel disposed within the machine surrounded by but spaced from the blades, the container, blades and mandrel, singly or in combination, being rotatable around a common longitudinal axis.

Referring now to the drawing, there is shown one embodiment of an etching apparatus in accordance with the present invention comprising a vertically disposed rotatable cylinder 10 with a top 12 adapted to receive etching solution and a closed bottom 14 (except for an outlet) said cylinder being adapted to contain an etching fluid. A drive means such as, e.g., a pulley, belt and motor assembly 16 is provided to rotate the container. Longitudinally disposed within the container 10 is a circular array of blades 18 all disposed parallel'to the container wall 19 with each blade 18 having a similar arcuate crosssection. These blades 18 are adjustable either singly or as a group to one of various possible angles, usually predetermined, with respect to the transverse axis of a mandrel, described hereinafter. Circular header rings 20 and 22 both at the bottom and top couple said blades 18 in a pivotal vertical position, such that each blade maintains its relative position except for the aforesaid change in angle. A mandrel 24 supported by an axle 26 and capable of holding a plate 28 to be etched is centrally located in the machine in a parallel spaced relationship to the blades 18. Conventional drive means, not shown, are provided to impart rotational movement to the array of blades 18 and/or mandrel 24.

Though the machine is depicted in a vertical attitude in FIGURE 2, it should be understood that it may be so-constructed and/or disposed to permit operation in a horizontal or inclined attitude if so desired.

In actual operation of the present centrifugal etching machine as shown, a powderless etching bath is prepared and charged into the container 10 through an opening therein, the outlet 30 at the other end of the apparatus being closed. Powderless etching baths which may be employed generally comprise a mineral acid, an organic filming agent and one or more organic solvents. Actual examples of such baths are disclosed and claimed in U.S. Patents 2,828,194; 2,979,387; 3,023,138, and 3,152,083. An etchable zinc or magnesium photoengraving plate 28, e.g., is then clamped to the mandrel 24 (clamps not shown in drawing) and the container 10 and etchant liquid 32 therein are caused to rotate rapidly about the plate 28 by drive means provided for this purpose. Upon being sufficiently rapidly rotated the etching fluid forms a liquid annulus 34 against the container wall 10. The blades 18, having been previously positioned so as to dip into the liquid annulus 34 a predetermined depth, scoop etchant fluid from the liquid annulus 34 and impinge same against the rotating plate 28.

In operating the apparatus of the present invention the etching fluid must not ordinarily impinge radially upon the plate since the rotary motion of the plate relative to the impinging fluid may distort the etched relief. Rather, the etching fluid should approach the plate almost tangentially at such a velocity as to be in substantial synchronism with the moving periphery of the plate when impingement occurs. The etching fluid can be applied in the foregoing manner by selecting any of numerous suitable combinations of plate rotation velocity, blade array rotation velocity, container rotation velocity, blade angle, and blade shape. The drawing depicts only one such combination.

The blades 13 may be operated in a fixed position and fixed angle, or, may also be caused to rotate as shown by the arrows in FIG. 1 of the drawing. In any event the blades 18 should operate to scoop etchant and vigorously impinge or splash it against the plate 28 in the aforesaid manner. The rotating plate upon being contacted with the etching fluid from the blades is continuously etched by the impinging fluid, whereupon, almost immediately the used etchant is centrifugally cast off with a force, e.g., several times that of gravity as, e.g., shown in FIG. 1. It is manifest that the plate 28 is rotated at a sufiicient rate to provide the necessary force to cast off or expel the etchant from the plate as described. This rate depends upon the diameter of the plate, of course. This etching operation is continued until the depth of etch on the plate 28 is obtained, as predetermined in previous runs.

If the etching fluid needs temperature adjustment, the aforesaid heating or cooling means, not shown in drawing, may be provided and operated as needed, either manually or automatically by thermostatic means.

The present apparatus provides a means of etching curved plates in the manner described to obtain a good quality etch which in general, is substantially equal to that obtained on fiat etched surfaces. Problems encountered heretofore in etching curved plates are thereby substantially minimized, if not eliminated, inasmuch as excess etchant does not run off the plate being etched by gravity flow but rather, the used or spent etchant is immediately expelled otf the plate by centrifugal force such that elongated image shoulders (tailing), and undercutting are essentially reduced to zero.

The terms curved plate or curved segment as used herein refers broadly to etchable curved surfaces in general used for engraving and in printing and include, e.g., magnesium or zinc plate, sheet, thin wrap-around sheet, extruded tubing, extruded cylinders, impact extruded cans, thin wrap-around foil, and the like.

Various modifications can be made in the present invention without departing from the spirit or scope thereof and it is understood that the invention is only limited as defined in the appended claims.

I claim:

1. A method of etching curved plates comprising the steps of: rotating a liquid annulus of etching solution against a continuous internal wall of a cylindrical container; longitudinally positioning a rotatable curved plate to be etched inwardly from said liquid annulus and spaced therefrom; intercepting the inner surface of said liquid annulus with a circular array of curved longitudinally extending blades thereby impinging said liquid inwardly of the annulus toward the curved plate, said blades being adjusted at a predetermined rotational angle whereby the inwardly directed liquid impinges tangentially upon the curved plate, and rotating said curved plate on its axis rapidly enough to flng etching solution from the surface thereof.

2. The method of claim 1 wherein the liquid annulus and curved plate are rotated in an opposite direction to the circular array of blades.

3. An etching machine comprising in combination: a rotatable cylindrical container, the ends thereof being adapted to retain an etching liquid in said container; a rotatable circular array of longitudinal, cross-sectionally curved blades positioned internally within the container, each of said blades being spaced apart and from the container, all said blades being coupled at their respective ends to a header member by means carried by said header members to adjustably position said blades at a desired angle with respect to the transverse axis of the machine; the assembly of blades and headers being rotatable; a rotatable work holder longitudinally disposed and centrally supported in the machine in a spaced relationship to said blades, said work holder being adapted to maintain and rotate a curved plate; means for individually rotating said cylinder, blades and holder of the etching machine; and inlet and outlet means carried by the containerfor introducing and discharging etching solution.

4. An etching machine comprising a cylindrical container; a circular array of blades longitudinally disposed therein in a spaced relationship to the container; and a longitudinal work holder disposed within the machine surrounded by but spaced from said blades, the container blades and holder singly or in combination, being rotatable about a common longitudinal axis.

References Cited UNITED STATES PATENTS 3,108,031 10/1963 Hasala et a1. 156345 3,232,814 1/1966 Ruttan et a1 156345 JACOB H. STEINBERG, Primary Examiner U.S. CL. X.R. 

